Semisolid metal injection molding machine components

ABSTRACT

The present invention provides an alloy for components of semi-solid injection molding machinery. In particular, the alloy is a intermetallic-hardened steel, known as a Maraging steel alloy. The Maraging steel alloy includes Cr, Co, Mo, and about 0.15% or less by weight C.

BACKGROUND

The present invention relates to alloys for semi-solid and liquidinjection molding and die casting machine components and components madefrom such alloys.

Generally semi-solid metal injection molding is the process whereby analloy feedstock is heated, subjected to shearing and injected under highpressure into a mold cavity. Heating brings the feedstock into a statewhere both solid and liquid phases are present while the application ofshearing forces prevents the formation of dendritic structures in thesemi-solid alloy. In this state, the alloy may exhibit thixotropicproperties.

The feedstock may be received into the barrel of the semi-solid metalinjection molding machinery in one of three forms: liquid, semi-solid orparticulate solid. The former two forms require additional equipment andspecial handling precautions to prevent contamination of the alloymaterial and therefore increase costs. The latter form, while being moreeasily handled, results in longer cycle times and significant thermalgradients in the first encountered portions of the barrel and morepronounced thermal shock to that portion of the barrel.

More specifically, semi-solid metal injection molding (SSMIM) involvesthe feeding of alloy feedstock into the barrel of the semi-solid metalinjection molding machinery. In the barrel, the alloy feedstock isheated and subjected to shear, often by rotating a screw or paddleslocated therein. As a result of heating and shearing, the temperature ofthe alloy feedstock is raised so as to be above its solidus temperatureand below its liquidus temperature. Within this temperature range, thefeedstock is transitioned into semi-molten material having co-existingsolid and liquid phases. In addition to aiding to heating, shearingfurther prevents the formation of dendritic structures in the alloy. Inthis thixotropic state, the semi-solid alloy material is injected,either through reciprocation of the screw or transfer and reciprocationof a plunger to a shot sleeve, into a mold cavity and solidified to formthe desired part.

Typically, components for the injection molding machine are formed fromconventional carbon-hardened steels. These steels, however, are not verytough and are not truly weldable. These steels temper back at servicetemperatures of about 1200° F., thus softening. When these steels areformed into components for an SSMIM machine, such as check rings, theysplit from the radial impact fatigue stresses. Many failures haveoccurred in other types of components such as screw tips, piston rings,push rings, flanges, barrels and screws due to this marginal toughness.Some of the failures of check rings and push rings appear to beaggravated by the heat affected zone under weld deposits. These steelsare also susceptible to embrittlement during “torching” when operatorstend to overheat the components by gas torches, causing components suchas nozzles to fail by a brittle mode at the flange, as well as bybulging and splitting longitudinally.

Thus, welding of these carbon hardened alloys is prone to variation inthe skill of the welder. Careful pre-and post-heating is required toprevent cracking in the heat-affected zone of the steel. Even with goodpractice, however, the toughness of the heat affected weld zone appearsto be quite inferior to the base steel.

As seen from the above, there exists a need for an improved material forcomponents of an SSIMM machine and component made of such material.

SUMMARY

In satisfying the above need, as well as overcoming the enumerateddrawbacks and other limitations of the related art, the presentinvention provides an alloy for components of semi-solid injectionmolding machinery. In particular, the alloy is a intermetallic-hardenedsteel, known as a Maraging steel alloy. The Maraging steel alloyincludes Cr, Co, Mo, and about 0.15% or less by weight C.

Since during welding of these alloys, the heat-affected zone is bothsoft and tough, these maraging steels are very weldable. Thisheat-affected zone can be returned to the hardness and toughness of thebase alloy by simple post-weld aging, thus avoiding the three-stagetemper treatment cycle commonly employed for conventional carbonhardened steels. To save heat treating costs, the aging can beaccomplished in start up of a machine.

Further features and advantages of this invention will become readilyapparent to persons skilled in the art after a review of the followingdescription, with reference to the drawings and claims that are appendedto and form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of one version of a semi-solid metalinjection molding machine with which the present invention may beutilized;

DETAILED DESCRIPTION

Referring now to the drawings, seen in FIG. 1 is an apparatus/machine 10used for semi-solid metal injection molding (SSMIM). The construction ofthe machine 10 is, in some respects, similar to that of a plasticinjection molding machine.

The machine 10 includes a feed hopper 11 for the accommodation of asupply of pellets, chips, or powder of a suitable metal alloy at roomtemperature. For purposes of describing the salient features of thesubject invention, magnesium alloys will be referred to as examples ofsuitable metal alloys that may be used in practicing the invention. Aland Zn are other such alloys.

A suitable form of feeder 12 is in communication with the bottom of thehopper 11 to receive pellets therefrom by gravity. The feeder 12includes an auger (not shown) which functions to advance pellets at auniform rate from the feeder 12. The feeder 12 is in communication witha feed throat 13 of a barrel 14 through a vertical conduit 15 whichdelivers a quantity of pellets into the barrel 14 at a rate determinedby the speed of the feeder auger. An atmosphere of inert gas ismaintained in the conduit 15 and barrel 14 during feeding of the pelletsso as to prevent oxidation thereof. A suitable inert gas is Argon andits supply is effected in a conventional manner.

As is conventional in a thermoplastic injection molding machine, barrel14 accommodates a reciprocable and rotatable screw 16 provided with ahelical flight or vane 17. Adjacent the discharge end of the barrel, thescrew has a non-return valve assembly 18 and terminates in a screw tip19. The discharge end of barrel 14 is provided with a nozzle 20 having atip 20 a received and aligned by a sprue bushing mounted in a suitabletwo-part mold 22 having a stationary half 23 fixed to a stationaryplaten 24. The mold half 23 cooperates with a movable mold half 25carried by a movable platen 26. The mold halves define a suitable cavity27 in communication with the nozzle. Mold 22 may be of any suitabledesign including a runner spreader 28 in communication with the cavity27 and through which the semi-solid material may flow to the cavity inthe mold. Although not shown in the drawings, suitable and conventionalmold heating and/or chilling means may be supplied if required.

The opposite end of injection molding machine 10 includes a known formof high speed injection apparatus A including an accumulator 29 and acylinder 30 supported by stationary supports 31 on a suitable supportsurface S. Downstream from the cylinder 30 a shot or injection ram 32projects into a thrust bearing and coupler 33 for operational connectionin known manner with a drive shaft 34 for the rotary and reciprocablescrew 16. Thrust bearing and coupler 33 may separate the shot ram 32from drive shaft 34 so that shot ram 32 may merely reciprocate and notrotate when desired. Drive shaft 34 extends through a conventional formof rotary drive mechanism 35 which is splined to drive shaft 34 topermit horizontal reciprocation of drive shaft 34 in response toreciprocation of shot ram 32 while the drive shaft 34 rotates. Thisshaft is in turn coupled with the screw 16 through a drive coupling 36of known type to transmit rotation to the screw 16 as well as high speedaxial movement within barrel 14 in response to operation of high speedinjection apparatus A. It will be understood that suitable andconventional hydraulic control circuits will be used in the conventionalmanner to control the operation of injection molding machine 10.

Typically, operation of injection molding machine 10 involves rotationof the screw 16 within the barrel 14 to advance and continuously shearthe feed stock supplied through feed throat 13 to a materialaccumulation chamber C between the screw tip 19 and the nozzle. Suitableheating means of a type to be described supply heat to barrel 14 toestablish a temperature profile which results in conversion of the feedstock to a slushy or semi-solid state at a temperature that is above itssolidus temperature and below its liquidus temperature. In thissemi-solid state the material is subjected to shearing action by thescrew 16 and such material is continuously advanced toward the dischargeend of the barrel to pass the non-return valve 18 in sufficientaccumulated volume ultimately to permit high speed forward movement ofthe screw 16 to accomplish a mold filling injection or shot. High speedinjection apparatus A functions at the appropriate time (in a manner tobe explained) to move shot ram 32 forwardly, or toward the discharge endof the barrel 14, which results in forward movement of the thrustbearing 33 and drive shaft 34. Since drive shaft 34 is coupled to theshaft of the screw 16 through coupling 36, extrude screw 16 movesforward quickly to accomplish the mold filling shot. Non-return valveassembly 18 prevents the return or backward movement of the semi-solidmetal accumulated in the chamber C during the mold filling shot.

As opposed to other methods of semi-solid molding, the above describedmethod has the advantage of combining slurry generation and mold fillinginto a single step. It also minimizes safety hazards which occur whenseparately melting and casting reactive semi-solid metal alloys.Obviously, and as will be further appreciated, the alloy of the presentinvention will have utility with machines other than the one of theillustrated variety. By way of illustration and not of limitation, suchother variety machines and apparatus include two stage machines andplastic injection molding machines, similar to die casting machines,where slurry generation and injection molding occur in separate portionsof the apparatus, and non-horizontally oriented machines. Additionally,it will be understood by those skilled in the art that other mechanismscould be used to advance the material in the barrel (including gravity),that other mechanisms could be used to induce shear (such as rotatingpaddles, fins or electromagnetic fields) and that other mechanisms couldbe used to eject the material from the machine (such as a plunger of ashot sleeve). Furthermore, alloys of this invention can be applied toall-liquid injection molding and die casting.

The barrel 14 of the machine 10 is divided along its length into aseries of different heating zones, with the exact number of zones being,to a certain extent, a matter of design choice. Proceeding from the endof the barrel 14 where the feedstock is received, the respective heatingzones are increasingly hotter until leveling out in the latter half ofthe barrel 14. The barrel temperatures may be measured by a thermocouplepositioned approximately three-quarters of the way through the barrel(towards the interior of the barrel).

The feedstock may be designed to exhibit a gradual melting reaction tomatch the desired temperature profile along the barrel 14. In thismanner, processing of the feedstock material is done while impartingvigorous shear to the semi-solid, avoiding plugs, reducing thermal shockand stress on the barrel and while being able to precisely fix thefraction solids in the subsequently molded part.

Such a feedstock enables faster cycle times while decreasing thermalshock and stress on the machine 10. A preferred feedstock exhibits amild on-setting of melting or a spreading of the eutectic reaction overa larger temperature range when initially introduced into the barrel.This decreases the thermal shock in the initial portion of the barrel,and, further, upon the on-set of melting and the introduction of theliquid phase in the feedstock, thermal transfer is enhanced and furthermelting is activated.

In accordance with the invention, various components of the machinery 10are made of intermetallic-hardened steels, referred to as Maragingsteels formed by martensite aging, rather than conventionalcarbide-hardened steels. These alloys are hardened by nano-sizedintermetallic precipitates within a soft and tough martensite matrix,rather than coarse carbide phases that form a brittle martensite matrixthat occurs in conventional steels. The intermetallic precipitates aremore resistant to softening than carbides at barrel temperatures of 1100to 1200° F.

Components formed of Maraging type steels are very weldable in that theheat-affected zone is both soft and tough. This zone can be returned tothe hardness and toughness level of the base alloy by simple post-weldaging at, for example, about 900° F. for about 3 hours, thereby avoidingthe long and rigorous quench and three stage temper treatment cycleassociated with conventional steels. Furthermore, dimensional changesthat occur during aging are minimal, such that final machining can bedone in the soft annealed state before hardening and aging may beaccomplished in machine start-up. These steels are also designed withsufficient Cr to resist oxidation at the service temperatures of themolding machine 10, while also resisting liquid Mg attack.

Shown below in Table 1 is a comparison of conventional carbon hardenedsteels (first four entries), referred to hereinafter as C steels, withMaraging steels (next nine entries): TABLE 1 Composition (wgt. %) SteelType C Cr Co Mo W Ni Other H-11 C .40 5.0 — 1.3 — — 0.5V H-13 C .40 5.2— 1.3 — — 1.0V T-2888 C .20 9.5 10.0 2.0 5.5 — — Volvic 10 C .18 10.010.0 — 6.5 — — T-30 Maraging + C .14 14.7 13.0 5.0 — — 0.3V T-31Maraging .03 14.0 12.0 5.0 — 4.0 — X14N4K14M3T Maraging .02 14.0 13.03.0 — 4.0 0.3Ti Russian Maraging .02 12.0 14.0 5.0 — 5.0 — AFC-260Maraging + C .08 15.5 13.0 4.3 — 2.0 0.14Nb D.70 Maraging <.03 12.0 14.54.0 — 4.3 Ti, Nb, Al, B, Zr Pyromer X-15 Maraging <.01 15.0 20.0 2.9 — —— Pyromer X-23 Maraging <.03 10.0 10.0 5.5 — 7.0 — Ultrafort 403Maraging <.02 11.0 9.0 4.5 — 7.7 0.4Ti, 0.15Al Preferred Range <.0312-15 10-14   4-5.5 — 0-5 0-.5Ti, 0-.2Al, 0-.5V, 0-.2Nb Broad Range<.03-.15  9-16  9-20 2.9-6 — 0-8 0-.5Ti, 0-.2Al, 0-.5V, 0-.2Nb

In general, Maraging types of steel employ a Co/Mo hardening mechanism.As to hardening precipitates, the T-30 composition, for example, usescarbides of M₂₃C₆ that precipitate at about 900° F.; but overage,however, at about 1200° F. The T-31 composition is precipitationhardened by the more stable Laves, R and Chi phases (Fe,Cr,Co,Mointermetallics) which precipitate at about 1200° F. in fine arrays thatare most resistant to overaging and softening.

The T-31 composition has soft and ductile martensite matrix which formsnear room temperature upon cooling from the austenite matrix that existsduring solution treatment at about 1900° F. Moreover, using the T-31composition avoids the delta phase during annealing. In contrast tocarbon hardened steels, severe quenching is not be needed after solutiontreatment of the T-31 composition. That is, air cooling may suffice totransform the alloy to martensite. In some implementations, to obtaincomplete transformation of austenite to martensite, refrigeration can beused. The transformation defects in the martensite help nucleatenanometer precipitates upon Maraging (martensite aging) between about900 and 1200° F. The soft martensite (having a hardness of about 30 Rc)can be formed, welded and machined before final aging which provides ahardness up to about 67 Rc. Dimensional changes that occur during finalaging are less than 0.0001 in/in compared to +0.0006 in/in for C steels.

During subsequent heating at 10000 to 1250° F., martensite reverts toaustenite in a time dependent mode. Some reverted austenite of about 5to 15% improves the toughness. This reverted austenite is of nanometerdimensions but still contains the fine precipitates and is still strongwhile acting as a tough crack stopper. Note, however, that morereversion softens the steel. Thus, to obtain sufficient life spans forthe machine components, the Maraging steels are alloyed to obtain theproper amount of reverted austenite. In accordance with the invention,preferred ranges for the composition of the various alloying elementsare listed as the fourteenth entry of Table 1, and broad ranges arelisted in the last entry of the table. It is advantageous to stabilizethe alloy at 1250° F. before service. It is feasible to rejuvenate usedcomponents to extend their life, by re-annealing at 1500 to 1900° F.followed by aging/stabilizing at 1100 to 1250° F.

The alloying elements in the Maraging steels provide at least thefollowing benefits:

-   -   a. Cr imparts oxidation resistance and participates in the        hardening intermetallic and carbides. For example, raising Cr        from 5 to 15% diminishes oxidation in 300 hrs at 1200° F. from        3.81 to 0.32 mg/cm2.    -   b. Cobalt prevents embrittling delta formation, maintains        martensite transformation above room temperature, speeds the        aging reactions, participates in the intermetallic hardening        phases, and slows formation of too much austenite at 1200° F.    -   c. Mo, in synergism with Co, participates in the intermetallic        hardening phases. Moreover, Mo in synergy with Cr enhances the        stability of the carbide phase.    -   d. C provides for hard, brittle martensite and introduces the        delta phase. Thus, the delta phase increase as the amount of C        increases.    -   e. Ni toughens the martensite phase. Note, however, too much Ni        depresses the martensite transformation temperature and the        austenite reversion temperature.

Heat treatment, for example, stabilizing heat treatment or regeneratingheat treatment, of molding machine components made of the Maragingsteels offers flexibility in obtaining a desired life span of thecomponents. Solution temperature can be from 1500° F. to about 1900° F.The higher temperatures dissolve the coarse precipitates and minimizethe delta phase. Aging temperature and time can be designed to providefine precipitates along with 5 to 15% reverted austenite. A pre-serviceaging treatment at about 1200° F. serves to stabilize the age hardeningreaction to prevent over-hardening or softening at lower servicetemperatures. For example, aging at 1200° F. in one grade providescomponents with a hardness of about 40 Rc, which does not change duringservice times of 200 hrs at 1200° F.

Surface treatment also provides certain benefits to Maraging steels. Forexample, gas nitriding in NH₃ increased surface hardness by 20-30%,while boosting fatigue life, rolling contact life and wear resistance.Ion nitriding may improve wear resistance by 100-150%. In contrast, suchnitriding treatments may embrittle the marginally tough C steels, sothat such treatments may not be useful on these alloys.

Table II below illustrates the hardness stability of the T-31 alloy ascompared to conventional C steel (H-13): TABLE II LOSS OF HARDNESSDURING SERVICE Hardness After Original 25,000 cycles to Alloy Hardness,Rc 1250° F., Rc ΔHardness, Rc H-13 46 31 15 T-31 48 43 5

Thus, H-13 as well as H-11 are not strong enough for the rigorous wear,impact and fatigue exposure of certain machine components. Furthermore,they soften and oxidize very quickly at 1200° F.

As for the T-2888 and Volvic 10 alloys, these suffer from low toughness,as measured by Charpy v-notch (CVN) impact energy tests, and softening.Thus, components such as screws 16, barrels 14 or sections thereof,nozzles 20, nozzle flanges, screw tips, screw adaptor, check rings,piston rings and push rings made of Volvic 10 may experience failures atundesirable rates. For example, check rings and piston rings made ofVolvic 10 may require replacement after 40,000 to 50,000 cycles ofmachine operation. Not only are replacement parts costly, but the downtime associated with replacing the parts raises the production costsvery significantly.

Examples of semi-solid injection molding machinery components made ofMaraging steels in accordance with the invention have been testedwithout failing include:

-   -   A. Nozzle made of T-30: After 5000 cycles, the nozzle retained        its original hardness at 40 Rc, bulged a slight 1.5% and did not        oxidize significantly. This compares to the conventional carbon        hardened steel Volvic 10 which softened from the original 45 Rc        to 20 to 35 Rc and bulged 1% in 3000 cycles.    -   B. Piston rings made of T-30: After 5000 cycles, the rings        retained a hardness at 47 Rc and were ductile enough to be        removed. In contrast, Volvic 10 rings embrittle in service and        then fracture upon removal.    -   C. Check rings made of T-31: After 7000 cycles, no distress was        observed; hardness retained at 40 Rc; some pitting on seal face        observed.    -   D. Push ring made of T-31: After 3000 cycles, no distress was        observed, hardness retained at 47 Rc.

Thus, in accordance with the invention, the Maraging and Maraging +Calloys are useful for machine components such as hot runners, hotsprues, nozzles, nozzle retaining flanges, barrel end caps, barrels,barrel liners, screw tips, check rings, piston rings, push rings, screwextensions and screws.

Referring now to Table III, the mechanical properties of theconventional carbon hardened steels (first three entries) are comparedwith that of some of the Maraging steels (last five entries): TABLE IIIMECHANICAL PROPERTIES Aging UTS, YS, UTS @ R.S, 100 hr @ Temp, 1000 1000RA CVN, 1100 F. 1100 F. Alloy F. psi psi El, % % ft-lb KIC Rc KSI KSIH-13 10 50 T- 1200 223 180 5 49 124 2888 Volvic 1200 260 190 5 48 130 10T-30 1100 290 214 10 32 9 23 53 176 80-90 700 255 200 17 52 18 50 50T-31 960 215 33 49 AFC260 1000 254 228 14 44 61 140 60 800 224 188 20 5692 Pyromet 900-1050 258 237 15 58 18 70 50 <140 X-23 Ultrafort 895 245242 10 60 25 49-61 120 403where UTS is the ultimate tensile strength, YS is the yield strength, Elis the elongation, RA is reduction in area, CVN is the Charpy v-notchimpact energy, Kic is the fracture toughness, Rc is the Rockwellhardness, and R.S. indicates the rupture strength.

Of particular note is that with a hardness between 48-50 Rc, the roomtemperature toughness of Maraging steel is the highest at 33 ft-lb (CVNimpact energy), with Maraging plus C being lower at 18 ft-lb, andconventional C hardened T2888 and Volvic 10 being even lower at 5 ft-lb.

As a person skilled in the art will readily appreciate, the abovedescription is meant as an illustration of implementations of theprinciples of this invention. This description is not intended to limitthe scope or application of this invention in that the invention issusceptible to modification, variation and change, without departingfrom spirit of this invention, as defined in the following claims.

1. A semi-solid injection molding machine, comprising: a plurality ofcomponents defining a flowpath through the machine for a feedstock, atleast one of the plurality of components being constructed of amartensitic Maraging steel alloy material Including Cr, Co, Mo, andabout 0.15% or less by weight C.
 2. The machine of claim 1 wherein theMaraging steel alloy includes between about 9 and 16% by weight Cr. 3.The machine of claim 2 wherein the Maraging steel alloy includes betweenabout 12 and 15% by weight Cr.
 4. The machine of claim 1 wherein theMaraging steel alloy includes between 9 and 20% by weight Co.
 5. Themachine of claim 4 wherein the Maraging steel alloy includes betweenabout 10 and 14% by weight Co.
 6. A semi-solid injection moldingmachine, comprising: a plurality of components defining a flowpaththrough the machine for a feedstock, at least one of the plurality ofcomponents being constructed of a martensitic Maraging steel alloymaterial including Cr, Co, Mo, and about 0.15% or less by weight C.wherein the Maraging steel alloy includes Mo in the range of about 2.9and about 6% by weight Mo.
 7. The machine of claim 6 wherein theMaraging steel alloy includes Mo in the range of about 4 and 5.5% byweight.
 8. The machine of claim 1 wherein the Maraging steel alloy hasan austenite state at about 1500-1900 ° F.
 9. The machine of claim 8wherein the Maraging steel alloy martensite ages at between about 900and 1200° F.
 10. The machine of claim 1 wherein the Maraging steel alloyhas a hardness of about 40-50 Rc.
 11. A semi-solid injection moldingmachine comprising: a barrel which receives feedstock and heats thefeedstock; a nozzle from which feedstock in a semi-solid state isejected; means for advancing the feedstock within the barrel; means forsubjecting the feedstock to shear; means for ejecting feedstock from thenozzle; wherein one of barrel, nozzle, means for advancing, means forsubjecting, and means for ejecting are constructed of a martensiticMaraging steel alloy material including Cr, Co, Mo, and about 0.15% orless by weight C.
 12. The injection molding machine of claim, 11 whereinthe Maraging steel alloy includes between about 9 and 16% by weight Cr.13. The Injection molding machine of claim 12 wherein the Maraging steelalloy includes between about 12 and 15% by weight Cr.
 14. The injectionmolding machine of claim 11 wherein the Maraging steel alloy includesbetween 9 and 20% by weight Co.
 15. The injection molding machine ofclaim 14 wherein the Maraging steel alloy includes between about 10 and14% by weight Co.
 16. A semi-solid injection molding machine comprising:a barrel which receives feedstock and heats the feedstock; a nozzle fromwhich feedstock in a semi-solid state is ejected; means for advancingthe feedstock within the barrel; means for subjecting the feedstock toshear; means for ejecting feedstock from the nozzle; wherein one ofbarrel, nozzle, means for advancing, means for subjecting, and means forejecting are constructed of a martensitic Maraging steel alloy materialincluding Cr, Co, Mo, and about 0.15% or less bv weight C wherein theMaraging steel alloy includes Mo in the range of about 2.9 and about 6%by weight.
 17. The injection molding machine of claim 16 wherein theMaraging steel alloy includes Mo in the range of about 4 and about 5.5%by weight.
 18. The Injection molding machine of claim 1 wherein theMaraging steel alloy has an austenite state at about 1500-1900° F. 19.The injection molding machine of claim 18 wherein the Maraging steelalloy martensite ages at between about 900 and 1200° F.
 20. Theinjection molding machine of claim 1 wherein the components are formedby all-liquid injection molding.
 21. The injection molding machine ofclaim 1 wherein the components are formed by die casting.
 22. Theinjection molding machine of claim 1 wherein the components are heattreated.
 23. The injection molding machine of claim 22 wherein the heattreatment is stabilizing heat treatment.
 24. The injection moldingmachine of claim 22 wherein the heat treatment is regenerating heattreatment.
 25. A semi-solid injection molding machine comprising; aplurality of components defining a flowpath through the machine for afeedstock, at least one of the plurality of components being constructedof a martensitic Maraging steel alloy material including Cr, Co, Mo,about 0.15% or less by weight C and about 8% or less by weight Ni.